The use of magnetic techniques for separating ferromagnetic materials from background substances has been known for quite some time. Recent refinements of such techniques have made it possible to precipitate hyperfine ferromagnetic wear particles from a lubricant sample taken from a machine, such as a diesel engine, and to determine the wear condition of the machine by optical analysis of such particles. A detailed description of apparatus and procedures for performing such precipitation and analysis is set forth in U.S. Pat. No. 4,047,814, issued on Sept. 13, 1977 to Vernon C. Westcott. Specifically, a lubricant sample is flowed along a shallow channel in an inclined glass substrate positioned over a magnet, the air-gap of which is aligned with the longitudinal axis of the substrate. Ferromagnetic wear particles are drawn by magnetic force down from the lubricant liquid so as to deposit onto the substrate surface. The substrate is typically in the form of a thin rectangular glass slide, provided with a pair of spaced parallel Teflon.RTM. strips secured to the edges of the slide to define a central liquid flow channel along the dimension of the slide. In carrying out this procedure with ferromagnetic wear particles, the larger particles are precipitated first, and the smaller particles are precipitated further along the flow path. Analysis, for example, by microscope, of the relative proportions of large and small size wear particles provides significant information about the state of wear of the machine from which the lubricant sample was taken.